Traffic and transport
Roads, vehicles, public transport and aviation. 5 sources, 2 international. 2 queued.
Sources

NDW live traffic data
Speeds and volumes from tens of thousands of road sensors, refreshed every minute. Also roadworks and incidents.
NS travel information
Live departures, delays and disruptions on the Dutch railways. Free, with a key from the NS API portal.

OpenSky Network
Aircraft positions picked up by a global network of receivers. Without an account, limited to current positions.

OpenStreetMap
Roads, buildings, shops, benches and cycle paths, mapped by volunteers. Very complete in the Netherlands, partly because the BAG was imported.

RDW registered vehicles
Data on every Dutch licence plate: make, model, fuel, weight and inspection expiry. No personal data.
In the queue
These sources are coming to this topic soon.
- NOV-data (NDOV-loket)NDOV
Timetables and live positions of buses, trams and metros.
- SSchiphol vluchtgegevensSchiphol
Flights, destinations and runway use.